1. Field of the Invention
The present invention relates to an electronic apparatus and a signal disconnection/connection method.
2. Description of the Related Art
Multifunction products that have a copy function, a FAX function, a print function, a scanner function, and the like have been often used in recent years. It has been known that, in such multifunction products, the power for unnecessary functions is turned off during the energy-saving mode so that the power saving of the system is achieved.
For example, Japanese Patent Application Laid-open No. 2003-234073 discloses an image processing apparatus that includes an engine control unit including a scanner control unit and a plotter control unit, a controller control unit that controls the entire apparatus, and a power supply unit (PSU) that controls the power supply to these units and in which the controller control unit and the engine control unit are connected to each other via a PCI bus and a FAX board can be connected to the PCI bus as an option.
The image processing apparatus has a stand-by mode, an engine-off mode, and a Suspend-To-RAM mode (STR) as energy-saving modes. The stand-by mode is a state in which the power of both the engine control unit and the controller control unit is turned on and is a mode that allows each operation (copy operation, scanner operation, and print operation) to be performed immediately. The engine-off mode is a state in which the power of the engine control unit is turned off and the power of the controller control unit is turned on and is a mode that allows communication such as a status notification to be performed between the image processing apparatus and an external device. The STR mode is a mode in which the power of the engine control unit is turned off and the power of the controller control unit is turned off except for some ICs thereof (the CPU is turned off).
In the image processing apparatus, the FAX board connected to the PCI bus as an option detects a ringing signal from a phone line so that it can perform a FAX communication with a caller. At that time, a binary signal is generated from the received ringing signal and, if its frequency falls within a detection range of a ringing frequency, it is recognized as a ringing signal.
A binary signal is generated in accordance with the rise/fall change of a ringing signal and, if the ringing signal is a sine wave, a clear binary signal is generated as shown in FIG. 13 and its frequency can be accurately measured. However, switching devices that output various ringing signals are available in the market, and some switching devices output a ringing signal with part of the waveform distorted, as shown in FIG. 14.
When the ringing signal output from the switching device is detected, a binary signal is split in accordance with the rise-fall-rise change of the distorted part. The frequencies of two binary signals on the positive and negative sides are concurrently measured so that, even if the waveform on one side is split as shown in FIG. 14, the frequency can be measured accurately by using the binary signal on the other side. However, for example, if both of the two binary signals are split as shown in FIG. 15, the frequency cannot be measured accurately using any of the binary signals; therefore, such a case can be resolved only by expanding the frequency detection range (for example, the upper limit frequency is increased up to 100 Hz).
If the CPU of the FAX board is turned on, the frequency detection range is expanded by software so that the frequency can be measured accurately even in the case shown in FIG. 15. However, if the CPU of the FAX board is turned off during the STR mode, the detection frequency cannot be controlled by software and the detection frequency depends on the capability of a device that detects a ringing signal from the phone line. Therefore, there is a possibility that the frequency of the binary signal does not fall within the detection frequency range. In this case, there is a possibility that the ringing signal is not recognized and a FAX communication with the caller cannot be performed. To prevent this situation, the CPU of the FAX board cannot be turned off even during the STR mode.
However, if the power of the FAX board is turned on during the STR mode, because the FAX board is connected to the controller control unit via the PCI bus, the current passes through the PCI bus and flows into the controller control unit from the FAX board, which can significantly affect the IC of the controller control unit.
Therefore, if the FAX board is connected, the controller control unit cannot shift to the STR mode. Thus, there is a problem in that the power consumption is increased (from 2.1 Wh to 16.1 Wh) because the FAX board is connected.